Eric Fischer creates maps using geotagged data from public sources. Here a map of San Francisco is formed by plotting the locations of Flickr pictures (red), Twitter tweets (blue), or both (white). What's interesting is that no underlying map outlines are used. The data itself is the map.
If you click through the link, you will see that readers have had fun highlighting areas they recognise, an example of leveraging a built-in Flickr feature to perform interactivity.
The title comes from the phrase promoted by the US Dept. of Homeland Security here.
